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Choosing an op-amp for your project

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Re: Choosing an op-amp for your project

#61

Post by kragen »

dragontamer wrote: post #59
kragen wrote: post #56

Earlier quoted context omitted.

That depends on what "most applications" means. I remember a paint program I saw in high school that some kids had written to draw sprites and backgrounds for their video games. The documentation explained that it could only edit 320×200×256 images, but that that should be adequate for "most projects". Depends on the context! In the contexts I'm thinking of, I would think that, if your load is drawing 5 amps of curre…

You're sniffing out the fact that I didn't have an exact application in mind when I wrote my earlier posts, lol. But yes, you are correct on this front. The more I post on this subject, the more I'm "backwardsly-targetting" a solar-powered MPPT circuit. Maximum Power Point Tracking circuits improve your solar-panel's efficiency by changing the current (through the use of a buck-boost converter, changing the voltage-a…

Oh, I see! And you might very plausibly be getting 5 amps at 0.7 volts or something there, if you're controlling a single solar cell? (I might be misunderstanding how they work.) If you're controlling a whole 200-watt panel it's less of an issue because usually they have several cells in series to get a more convenient output voltage.

I feel like a car's transmission or a bike derailleur may be a good analogy to explain it to people, though an MPPT tracker is a ratcheting CVT.

Re: Choosing an op-amp for your project

#62

Post by kragen »

dragontamer wrote: post #60
kragen wrote: post #57

Earlier quoted context omitted.

Oh, sure. You could totally build a chopper op-amp out of two discrete op-amps. I'd never thought about actually doing that...

I've seen designs that use a Chopper Op-Amp to actually auto-zero a power-OpAmp, effectively transferring the low Vos characteristics to a different OpAmp with completely different characteristics.

If the op-amp has a stable Vos I feel like maybe you could zero it by hand with a trimpot? You just need a button to short the inputs together while you're trimming it.

Re: Choosing an op-amp for your project

#63

Post by pjc50 »

kragen wrote: post #56
dragontamer wrote: post #54

Earlier quoted context omitted.

Accuracy is likely secondary. I expect that most applications are good with 1.5 digits (aka 95% accurate or so). You don't want to blow the entirety of this 5% allowable error on one micro-spec of one component, but I don't expect that most people especially need lots of accuracy here. The issue is that any circuit with 1 to 5 amps of current is a serious amount of power, meaning power efficiency is likely one of the…

That depends on what "most applications" means. I remember a paint program I saw in high school that some kids had written to draw sprites and backgrounds for their video games. The documentation explained that it could only edit 320×200×256 images, but that that should be adequate for "most projects". Depends on the context! In the contexts I'm thinking of, I would think that, if your load is drawing 5 amps of curre…

> I remember a paint program I saw in high school that some kids had written to draw sprites and backgrounds for their video games. The documentation explained that it could only edit 320×200×256 images

Sudden memories of https://en.wikipedia.org/wiki/Autodesk_Animator , which was commercial software with exactly those limits (due to inheriting them from VGA). Despite the limited resolution it had a spectacular array of features.

Re: Choosing an op-amp for your project

#64

Post by ckocagil »

magic_smoke_ee wrote: post #47
ckocagil wrote: post #29

Earlier quoted context omitted.

Potential replacements for ultra low THD would be: OPA1612, OPA1656 and OPA1642 with bipolar, cmos and jfet inputs respectively.

There's a massive (old) list of them in Horowitz & Hill TAOE 3e Table 8.3a p. 522. I'm sure you can just go to Digikey or Octopart and do a parameter search for high-voltage, low-noise, BJT-input op-amps too. If one wanted to "use a Ferrari to go the grocery store", they could always use a $20 AD797 or LT1115 for audio applications. :o)

I picked those particular chips is due to their extremely good performance at a reasonable cost. Check their THD against AD797 and LT1115! :)

Re: Choosing an op-amp for your project

#65

Post by bsder »

I'm really disappointed that the article didn't mention what is probably the single most important characteristic in an opamp when being chosen by an amateur:

Unity gain stable

Sure, the other characteristics are important, but a whole bunch of circuits that beginners are likely to use rely on opamps being unity gain stable. If they're not unity gain stable, the circuit will do very weird things, and a beginner won't know why.

Of course, debugging issues like that are how you eventually become an expert.

Re: Choosing an op-amp for your project

#67

Post by peteforde »

kragen wrote: post #45
peteforde wrote: post #7

I've watched the videos and agree that the OPA2323 does appear to sound amazing by subjective comparison to the TL071. However, it's not enough to say that it costs ~8.7x as much in local tokens because that doesn't reflect how much it costs as a percentage of the other components around it, many of which have a more profound impact on the outcome. This wouldn't stand as a good argument except that in many devices, y…

I think Zalewski's post is aimed at electronics hobbyists rather than high-volume producers or competitors. In that context, an OPA2323 might cost 98.99¢ https://www.digikey.com/en/products/detail/texas-instruments... vs. 7.958¢ for the TL071 https://www.digikey.com/en/products/detail/texas-instruments... but the Saturday afternoon you spend building and debugging your circuit costs hundreds of dollars in foregone in…

Quite possibly! I learn new things every day.

Re: Choosing an op-amp for your project

#68

Post by dragontamer »

kragen wrote: post #62
dragontamer wrote: post #60

Earlier quoted context omitted.

I've seen designs that use a Chopper Op-Amp to actually auto-zero a power-OpAmp, effectively transferring the low Vos characteristics to a different OpAmp with completely different characteristics.

If the op-amp has a stable Vos I feel like maybe you could zero it by hand with a trimpot? You just need a button to short the inputs together while you're trimming it.

This is necessary because Vos is often a voltage dependent inaccuracy. So as your circuit functions it's Vos is changing up and down.

Re: Choosing an op-amp for your project

#69

Post by squarefoot »

formerly_proven wrote: post #22
squarefoot wrote: post #15

Any comments on the LM4562? As per data sheet it appears to be really good for audio wrt noise and distortion, yet I see it rarely mentioned. https://www.ti.com/lit/ds/symlink/lm4562.pdf

It and the LME49720 (same part) were discontinued a couple years ago along with the entire LME Overture series.

You sure about the LM4562? I've just checked at TME, Mouser and Digikey, and all of them have many in stock. I's also marked as "nopb" so it could likely be a newer lead free version.

Re: Choosing an op-amp for your project

#70

Post by kevin_thibedeau »

nine_k wrote: post #52
blackguardx wrote: post #23

Earlier quoted context omitted.

Using Hall-effect sensors to measure current isn’t that common when currents are in the uA to mA range. I’ve also never seen them used even for Amp range measurements when the application is purely on-board power supply meaurement.

The example uses 5A. For mA range, of course not.

High current lab supplies routinely use current shunts for their self-measurement.
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